Fishermen, Scientists Question Bottom Water Properties in Relation to Lobster Migration

by Rebecca Clauss

(may appear in Commercial Fisheries News later this year)

Several years ago, Marc Palombo, a fisherman based out of Sandwich, MA and a member of the Atlantic Offshore Lobstermen's Association, picked up the phone to resolve a question that had been puzzling him for quite a while: "Why are my lobster catches in this region so low?" Eventually, he was directed to Jim Manning, a scientist from the Northeast Fisheries Science Center. As it turns out, Manning and Palombo had similar interests for different reasons. Manning has a particular interest in the physical oceanography of the Gulf of Maine and Georges Bank, while Palombo is curious how the physical environment affects lobsters in his region. After talking with Jim Manning, Marc Palombo was sent a temperature probe, which could be put on his lobster trap and left for months to record data. This is how the collaborative project Environmental Monitors on Lobster Traps (EMOLT) was born. The EMOLT project began in November 2000 with funding from the Northeast Consortium. It involves partners from the Atlantic Offshore, Massachusetts, Maine, and Downeast Lobstermen Associations. David McCarron, director of the Gulf of Maine Lobster Foundation, is responsible for coordinating much of the effort by training participants and assisting in data collection.

The underlying goal of the first phase of the project is to better understand the incidence and extent of temperature shift in the Gulf of Maine and Georges Bank region and to observe what type of effect these shifts may have on migratory lobster populations in the area. Approximately 50 temperature probes are now operational on lobster traps set out along the New England coast.

Results from Phase I show that bottom water temperature was especially cold off Georges Bank for this past season. Arthur Sawyer, Vice President of Massachusetts Lobster Association, has been equipped with one temperature probe during the first phase of the project and has recorded some interesting temperature data from his lobster trap. While located approximately 60 fathoms below the surface, Sawyer's probe detected a 3-4 °F drop during a storm, which occurred in early March. According to many lobstermen, this year's lobster hauls have been notably low, although, actual catches are not publicized. "Right now, some friends of mine are crying the blues," said Sawyer. Sawyer, like many lobstermen, feels that low lobster catches are linked to cold bottom water temperatures.

EMOLT participants Bill Adler and Marc Palombo have found that results from the first phase raised even more questions about the significance of salinity in lobster abundance and migration. In phase two of the project, salinity probes will be added to some of the lobster traps located along the coast. Salinity, although slightly more difficult and expensive to measure, is a much more effective tracer of freshwater intrusions, such as runoff due to melting snow and ice, heavy spring rains as well as input from remote source waters. Findings from earlier studies have shown that lobsters become stressed under low-salinity conditions and will migrate to deeper, saltier water in response to stormy weather (Jury et al., 1995; Jury et al., 1994). Whether or not these conclusions apply to the saltier environment outside the estuaries is still uncertain.

Initially, the primary focus of the project was on episodic or sporadic events (such as Gulf Stream rings, periods of upwelling or downwelling, storm events) and how they might impact lobster migration. But the project participants may be changing their tune. According to Manning, "Episodic events may be less important in controlling the lobster population in the long run." During a particularly cold season, such as this year's, "lobsters are more sluggish and likely to burrow, which may impact seasonal migration," said Manning. The project participants are now moving toward an inter-annual way of thinking. By concentrating more on year-to-year changes, the participants observe larger signals and can in turn make better conclusions concerning lobster movement and bottom water variability.

By measuring bottom water temperature and salinity in the coastal region of New England at fixed locations over multiple years, EMOLT participants may be able to determine whether longer-term processes such as climate change have more of an impact on lobster movement than smaller-scale events. In addition to studying the impacts of environmental factors on lobster populations, another major objective is to determine whether changes in temperature and salinity are related to local processes (such as river input and heating at the surface) or more remote inputs (such as ice melt from the north). In the future, this knowledge could be used to predict water mass movement and thus lobster migration.

The major sentiment shared by most of the participants is that EMOLT is a positive experience for building trust among scientists and fishermen. Bill Adler made an excellent point: "you have to produce science that everyone can agree on?Unlike groundfish, which everyone agreed the numbers were declining, scientists said that lobsters would collapse?which wasn't true," said Adler. Later on, states Adler, "the scientists told us 'maybe we were wrong.'"

McCarron expects to receive 8 salinity probes in the near future and will conduct a training session after the initial testing of these probes. The salinity monitors will be deployed along coast to examine the near-shore environment.

The project web site is at: emolt.html with links such as "Results from the Field" which allows users to click on particular sites on a map and view time series of temperature in relation to historical conditions.
 
 


Arnold Sawyer holding a temperature sensor.
 
 
 
 
 
 
 
 
 
 



 
 

TidBit temperature probe attached to a lobster trap






































For further information contact: James.Manning@noaa.gov

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